Energy absorbing arrangement

ABSTRACT

There is disclosed herein an energy-absorbing arrangement in which a plurality of outer thin-walled, cylindrical, tubelike, annular, ductile metal members are confined in a space between two body members. Each of the plurality of outer thin-walled energy-absorbing members has at least one additional, similar, inner thin-walled energy-absorbing member concentrically mounted within it in a nested relationship. The body members are adapted to have relative motion therebetween in a preselected direction. The spacing between the two body members is less than the unstressed diametral dimension of the outermost of the energy absorbing members, and therefore all of the energy-absorbing members are diametrally deformed under force by the two body members and relative motion of one body member with respect to the other in a preselected direction rolls the energy-absorbing members and thereby absorbs energy due to the cyclical plastic deformation or hysteretic deformation thereof. A nondeformable rigid retainer means may be positioned within the innermost of the energy-absorbing members to limit the diametral deformation thereof to prevent stress relieving plastic flow or creep of the energy-absorbing members.

[4 1 Mar. 7, 1972 [54] ENERGY ABSORBING ARRANGEMENT [72] Inventor: DavidL. Platus, 2001 l-lolmby Avenue,

Los Angeles, Calif. 90025 [22] Filed: Aug. 9, 1968 [21] Appl.No.:751,606

[52] US. Cl.... ..l88/l, 74/492 [51] Int. Cl ..Fl6d 63/00, 862d 1/16[58] Field of Search 188/1 C; 74/492; 293/5 LF,

Primary Examiner-Duane A. Reger Attorneyl'leizig & Walsh [57] ABSTRACTThere is disclosed herein an energy-absorbing arrangement in which aplurality of outer thin-walled, cylindrical, tubelike, annular, ductilemetal members are confined in a space between two body members. Each ofthe plurality of outer thin-walled energy-absorbing members has at leastone additional, similar, inner thin-walled energy-absorbing memberconcentrically mounted within it in a nested relationship. The

body members are adapted to have relative motion therebetween in apreselected direction. The spacing between the two body members is lessthan the unstressed diametral dimension of the outermost of the energyabsorbing members, and therefore all of the energy-absorbing members arediametrally deformed under force by the two body members and relativemotion of one body member with respect to the other in a preselecteddirection rolls the energy-absorbing members and thereby absorbs energydue to the cyclical plastic deformation or hysteretic deformationthereof. A nondeformable rigid retainer means may be positioned withinthe innermost of the energy-absorbing members to limit the diametraldeformation thereof to prevent stress relieving plastic flow or creep ofthe energy-absorbing members.

23 Claims, 16 Drawing Figures ENERGY ABSORBING ARRANGEMENT BACKGROUND OFTHE INVENTION l. Field of the Invention This invention relates to theenergy-absorbing art and, more particularly, to an improvedenergy-absorbing arrangement capable of providing comparatively highenergy absorption.

2. Description of the Prior Art In many energy-absorbing applications,it is desirable to absorb the energy associated with various phenomenainvolving relative motion of one member with respect to another. Suchapplications, of course, are quite prevalent and include, but are notlimited to, elevator safety override devices, steering wheelarrangements for automobiles to provide energy absorption therefrom onimpact in an accident, automobile bumper mountings, landing gear foraircraft and/or spacecraft, and the like.

Crushable or fragmenting tubes, honeycomb or cylindrical shells andother similar one-shot devices, have generally not been capable ofproviding the total energy absorption or the energy absorption ratedesired in a convenient packing arrangement of sizes applicable to manyof the above-described applications. Springs, on the other hand, whilecapable of many size modifications are generally of an energy absorbingand returning nature and do not, in a strict sense, absorb anappreciable amount of energy. Material transfer devices such ashydraulic shock absorbers, extrudable metal devices and the like,generally do not have a high absorption rate per unit weight or volumeassociated with the energy-absorbing device.

Various cyclic plastic deformation energy-absorbing devices, such asthose employing rolling solid toroidal elements have comparatively highenergy absorption characteristics per unit weight or volume but, ingeneral, such devices provide extremely limited design flexibility. Thatis, for a given energy absorption and cycle life, the size and weight ofsuch energy-absorbing arrangement is substantially fixed and in generalrequires comparatively high manufacturing tolerances. This, of course,results in a comparatively complex manufacturing technique andassociated high manufacturing cost.

Consequently, there has long been a need for a comparativelylightweight, high energy absorption rate arrangement that allowsconsiderable design flexibility and is comparatively insensitive totolerance variations and yet is comparatively easy and low in cost tofabricate.

SUMMARY OF THE INVENTION Accordingly, it is an object of applicantsinvention herein to provide an improved energy-absorbing arrangement.

It is another object of applicants invention herein to provide anenergy-absorbing arrangement in which design flexibility is provided.

It is yet another object of applicants invention herein to provide anenergy-absorbing arrangement that is comparatively easy to fabricate andcomparatively low in cost.

The above and other objects of applicants invention herein are achieved,according to one embodiment of applicants invention, by providing anenergy-absorbing element compressed between a first body member and asecond body member. The second body member is adapted to move in apreselected direction relative to said first body member maintaining thesqueeze force on the energy-absorbing element.

In this embodiment of applicants invention, the energy-absorbing elementabsorbs energy by the cyclic plastic deformation of a plurality ofdiametrally compressed tubelike or ringlike elements that are compressedalong a diameter thereof.

The energy absorbing element comprises an outer energyabsorbing membercomprising a thin-walled cylindrical tubelike annular ductile metalmember. The outer surface of the outer energy-absorbing member is infrictional rolling contact with the first bearing surface and the secondbearing surface as rolled in the squeezed or diametrallydeformedcondition therebetween during the relative movement of the second bodymember with respect to the first. The energy-absorbing element alsocomprises at least a first inner energy-absorbing member concentricallypositioned within the outer energy-absorbing member and the innerenergy-absorbing member is adapted to roll about the common axis thereofwith the outer energy-absorbing member, and the inner energy-absorbingmember comprising a thin-walled cylindrical tubelike annular ductilemetal member and the outer surface thereof is in contact with the innersurface of the outer energy-absorbing member.

The unstressed diametral dimension of the outer energy-absorbing memberis greater than the spacing between the first body member and secondbody member, so that both the outer energy-absorbing member and innerenergy-absorbing member are diametrally deformed by the first bodymember and second body member and are rolled therebetween during therelative movement in the deformed condition. Rolling in the deformedcondition subjects the outer energy-absorbing member and innerenergy-absorbing member to cyclic plastic deformation in which energyassociated with the relative movement is absorbed.

The outer energy-absorbing member may have an axial dimension greaterthan the axial dimension of the inner energy-absorbing member, the axialdimensions of the outer-and inner energy-absorbing members may be thesame, -or-the.

outer energy-absorbing member may have an axial dimension less than theinner energy-absorbing member.

In-other embodiments of applicants invention, the relative motionbetween the first body member and second body member may be linear or itmay be rotary.

In yet other embodiments of applicants invention, additional innerenergy-absorbing body members may be positioned within the tubelikeinner energy-absorbing member and the other additional innerenergy-absorbing members may besimilar thereto and also absorb energydue to the cyclic plastic deformation thereof during the relativemovement.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 illustrate oneembodiment of an energy-absorbing element useful in the practice ofapplicants invention herein;

FIG. 3 illustrates a thin-walled energy-absorbing member useful in thepractice of applicant's invention herein;

FIG. 4 illustrates a thick-walled energy-absorbing member;

FIGS. 5 and 6 are graphical representations of various characteristicsassociated with applicants invention herein;

FIG. 7 illustrates another energy-absorbing element useful inthepractice of applicants invention herein;

FIG. 8 illustrates another embodiment of applicants invention herein;

FIGS. 9 and 10 illustrate another embodiment of applicants inventionherein;

FIG. 11 illustrates another embodiment of applicants invention herein;

FIG. 12 illustrates another embodiment of applicant's invention herein;

FIGS. 13 and 14 illustrate another embodiment of applicants inventionherein;

FIG. 15 illustrates another energy-absorbing element useful in thepractice of applicants invention herein; and

FIG. 16 illustrates another embodiment of applicants invention herein.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As noted above, applicantsimproved energy-absorbing arrangement described herein absorbs energy bythe cyclic deformation of material exhibiting hysteretic stress-strainbehavior. Such energy absorption may be the cyclic plastic deformationof a ductile metal.

In applicants invention herein, the ductile metal utilized as theenergy-absorbing medium is generally in the form of a thin-walledcylindrical tubelike annular configuration having a preselected axiallength. The member is diametrally compressed; that is, the member iscompressed in the direction of its own diameter so that it is forcedinto a noncircular crosssectional shape. The energy-absorbing element isstrained well beyond its yield point and the relative motion of a firstbody member and second body member that provide the diametralcompression produces cyclic plastic bending deformation of theenergy-absorbing element thereby generating a substantially constantresisting force. Applicant prefers that the cylindrical energy-absorbingelements utilized in applicant's invention herein be thin-walled toprovide the thin-walled stressstrain characteristics associated with thehysteretic stressstrain behavior. Variations in diameter and wallthickness, as well as other parameters specific to the detailed designof energy-absorbing structures utilizing applicants improvedenergy-absorbing elements, are not critical and, consequently, a highdegree of design is provided for both high and low energy-absorbingcharacteristics in small or large spaces as may be required.

In the cyclic plastic straining of a ductile metal in a fixed strainrange, there is produced a hysteresis loop which stabilizes during thefirst few cycles. The repeated cycling results in almost constant energyabsorption per' cycle and until eventual fatigue failure. Since theplastic strain fatigue behavior of ductile metals generally follows asimple law relating plastic strain range, which may be considered thewidth of the hysteresis loop, and the fatigue life, the designcharacteristics combining the type of metal utilized for theenergy-absorbing means and the diameter of the energy-absorbing means,the wall thickness of the energy-absorbing means and the amount ofdiametral compression thereon can provide variations in both theenergy-absorbing characteristics as well as the length of life of theworking energy-absorbing means until failure. Further, according toapplicants invention herein, the nesting of a plurality of similarthin-walled, tubular, cylindrical annularlike energy-absorbing membersinside the outermost energy-absorbing member provides a great increasein energy-absorbing characteristics for a given design volume.

It will be appreciated that the narrower the hysteresis loop, whichimplies less energy absorption per cycle, the greater will be the numberof cycles that the energy-absorbing element may be subjected to beforefailure. Consequently, the greater the number of cycles, the greater thetotal energy absorption of the device. By providing the nestedarrangement of additional energy-absorbing elements, one within theother, in which each energy-absorbing member is thin-walled, a fargreater energy absorption for a given weight of material can be obtainedthan can be obtained for a corresponding member having a thick wallequivalent to the sum of the thin walls.

Referring now to FIGS. 1 and 2, there is shown one embodiment of anenergy-absorbing element useful in the practice of applicants inventionherein. The energy-absorbing element, generally designated 10, comprisesan outer energyabsorbing member 12 that is a thin-walled, cylindrical,tubelike, annular ductile metal member having a preselected wallthickness indicated by the letter t and a preselected axial lengthindicated by the letter 1,.

The outer energy-absorbing member 12 has an outer surface 14 and aninner surface 16. The thickness t is, of course, the distance betweenthe outer surface 14 and inner surface 16. The outer energy-absorbingmember 12 has a first preselected outer unstressed diametral dimension dto the outer surface 14 and a first preselected inner unstresseddiametral dimension d to the inner surface 16 thereof.

Nested within the outer energy-absorbing member 12 is a first innerenergy-absorbing member 18 that is concentrically mounted in the outerenergy-absorbing member 12 to have a common body member axis 22 thereof.The first inner energyabsorbing member 18 is also a thin-walled,cylindrical, tubelike, annular ductile metal member and it has apreselected wall thickness between an outer surface 24 thereof and aninner surface 26 thereof. The outer surface 24 thereof is insubstantially continuous contact, in this embodiment of applicantsinvention, with the inner surface 16 of the outer energyabsorbing member12.

The inner energy-absorbing member 18 has a second preselected outerunstressed diametral dimension to the outer surface 24 thereof, asindicated by the letter d;,, and the dimension (1;, is substantially thesame as the dimension d for the inner unstressed diametral dimension ofthe outer energyabsorbing member 12. Similarly, the innerenergy-absorbing member 18 has an inner unstressed diametral dimensionto the inner surface 26 thereof as indicated by d,.

If a squeeze force in the diametral direction is applied to theenergy-absorbing element 10, as indicated by the arrows 28, the outerenergy-absorbing member 12 and inner energy-absorbing member 18 aresubjected to a diametral squeeze force that deforms then diametrallyand, if while being subjected to this squeeze force they are rotated inthe direction indicated by the arrow 30 about their common axis 22,energy will be absorbed due to the cyclic deformation thereof. Further,if the deformation is in the plastic region of the materials from whichthe outer energy-absorbing member 12 and inner energy-absorbing member18 are comprised, there will be a cyclic plastic deformation during suchrolling motions.

In the embodiment of an energy-absorbing element 10 shown in FIGS. 1 and2, the axial length of I, of the outer energy-absorbing member is alsothe axial length of the inner energy-absorbing member 18. Further, itwill be appreciated, the ratio of the axial length of theenergy-absorbing members of applicants invention as described in theembodiments illustrated herein to the diameter thereof determineswhether the element may be considered a tube or a ring. That is, if theratio of the axial length to the diameter is 1:1 or less, then theenergy-absorbing element may be considered a ring. If the ratio of theaxial length to the diameter is greater than 1:1, the energyabsorbingelement may be considered a tube. In the embodiments of applicantsinvention shown herein, configurations thereof may include combinationsof both inner and outer tube and ring members with corresponding outerand inner ring and tube members or any combinations thereof, ashereinafter set forth. It will be appreciated that the difference indesignation is for convenience in description.

FIGS. 3, 4 and 5 illustrate the principles of the cyclic plasticdeformation of a thin-walled annular cylindrical ductile metalenergy-absorbing element, as contrasted with a thick-walled cylindricalannular ductile metal energy-absorbing element. As shown, FIG. 3illustrates a ductile metal thin-walled cylindrical annularenergy-absorbing element which, for example, may be similar to eitherthe outer energy-absorbing member 12 shown in FIG. 1, or the innerenergy-absorbing member 18 shown in FIGS. 1 and 2. The element 32 shownin FIG. 3 is subjected to diametrally directed compressive forcesindicated by the arrows 34 acting along a diameter thereof. As such, theenergy-absorbing element 32 is subjected to a particular stress-strainrelationship existing across the wall thickness from a point 36 on theouter surface 38 thereof to a point 40 on the inner surface 42 thereof.Curve A of FIG. 5 illustrates the strain distribution between the point36 and point 40 across the wall of the energy-absorbing element 32. Asshown on FIG. 5, it can be seen that Curve A is virtually a straightline and, therefore, the strain distribution across the wall thicknessfor a thin wall element is substantially linear. It will be appreciatedthat the thinner the wall with respect to the size of the diameter, themore nearly the Curve A in FIG. 5 approaches a true straight line. Sinceit is a desideratum to have a linear strain distribution across thewall, it can be seen that, according to principles of applicantsinvention herein, the thin wall energy-absorbing element provides aclose approximation to this desideratum. The more linear the straindistribution across the wall, the more optimum is the use of thematerial as an energy-absorbing element, and hence there is a greaterfatigue life or a greater number of cycles until failure for a givenspecific energy absorption in the energy-absorbing element 32. Thus, bydefinition, each of the energy-absorbing members utilized in applicant'sinvention is thin-walled to provide a substantially linear relationshipin the wall thereof at the desired stress loading. Applicant has foundthat this is generally achieved for most ductile metals when the ratioof wall thickness to outer diameter is equal to orless than onetenth.

FIG. 4 illustrates a correspondingly thick-walled energy-absorbingelement 44 subjected to diametrally directed squeeze forces 34 along adiameter thereof, and the magnitude of the forces illustrated by thearrows 34' is much greater than the magnitude of the forces illustratedby the arrows 34 in FIG. 3 for the same given specific energy absorptioncharacteristic as for the thin-walled member 32. Under such diametrallycompressive forces 34, the energy-absorbing element 44 is subjected toparticular stress and strain distributions in the wall thereof from apoint 46 on the outer surface 48 thereof to a point 50 on the innersurface 52 thereof.

Curve B in FIG. 5 illustrates the strain distribution across the wallfrom the point 46 to the point 50 for the energy-absorbing element 44.

From the above curves it can be seen that the strain at point 36 for theelement 32 shown in FIG. 3 is approximatelyequal, though, of course, ofopposite sign, to the strain at the point 40 on the inside surface 42.However, for the thick-walled element 44 shown in FIG. 4, as illustratedin Curve B of FIG. 5, it can be seen that there is a much greater strainat the point 50 on the inside surface 52 than at the point 46 on theoutside surface 48. Therefore, the thick-walled energy-absorbing element44 is not considered to have a linear strain distribution across thewall and thereby results in a less optimum use of material.Consequently, for the same specific energy absorption as required in thethin-walled energy-absorbing element 32 of FIG. 3, the thick-walledelement 44 shown in FIG. 4 will have a much shorter fatigue life untilfailure thereof.

FIG. 6 illustrates another characteristic of the thin-walledenergy-absorbing elements of applicants invention herein. As shown onFIG. 6, there is illustrated the relationship between the diametraldeflection and the required roll force. The roll force may be defined asthe force necessary to roll the energyabsorbing element, such as theenergy-absorbing element 10 shown in FIGS. 1 and 2, in a directionindicated by the arrow 30 while subjected to the squeeze forcesillustrated by the arrows 28. The diametral deflection may be defined asthe difference between, for example, the diameter d, which is theunstressed diameter to the outer surface 14 of the energy-absorbingmember 12 shown in FIGS. 1 and 2, and the stressed diameter which isless than the unstresseddiameter when the energy-absorbing element 10 issubjected to the squeeze forces 28. The Curve C in FIG. 6 represents therelationship for an energy-absorbing member having a first wallthickness, the Curve D of FIG. 6 represents the relationship for anenergy-absorbing element with a greater wall thickness than the elementillustrated by the Curve C, and. the Curve B represents the relationshipfor an energy-absorbing element having a greater wall thickness thantheenergy-absorbing element represented by the curve of FIG; D..TheCurve D.

represents a single thick-walled energy-absorbing element having a wallthickness equivalent to twice the wall thickness of the energy-absorbingelement illustrated by the curve C on FIG. 6.

The dashed line Curve F of FIG. 6 represents the relationship for anenergy-absorbing element similar to the energy-absorbing element 10shown in FIGS. 1. and 2, wherein the sum of the wall thicknesses t, andt; for the outer energy-absorbing element 12 and inner energy-absorbingelement 18 is equivalent to twice the thickness of the energy-absorbingelement illustrated by the Curve C of FIG. 6 and, therefore, has thesame total wall thickness as the wall thickness of the energy-absorbingelement illustrated by the CurveD of FIG. 6. From FIG. 6, therefore, itcan be seen that for a given roll force RF, the diametral deflection 54in the single thickwalled element illustrated by the Curve D is lessthan the deflection 56 required by produce. the same roll force RF forthe two thin-walled .nested energyfabsorbing elements. Further, it canbe seen that the. slope M, for the element represented by the Curve D issignificantly greater than the slope M; of the Curve F for the.twothin-walled elements. Hence, variations inenergyabsorption or rollforce with diametral deflection or tolerance changes will be less forthe two thin-walled elements than for thethick-walled element;

Therefore, dimensional tolerances for. the two thin-walledenergy-absorbing elements can be comparatively looser and thusmorenearly uniform energy absorption and roll force characteristics can .beobtained utilizing high mass production fabrication techniques.

Also, since the squeeze forces necessary to produce a particularspecific energy absorption or roll force 'are lower for the twothin-walled nested elements, as illustrated by the an energy-absorbingelement results Therefore, by utilizing two thin-walled members havingthe same total wall thickness as one thick-walled mernber, a moreoptimum strain distribution results and considerably lower; squeezeforces are required to produce the same average specific energyabsorption and hence roll force. This results in a lighter weightstructure and much longer cycle life for the same specific energyabsorption per cycle. Conversely, for a given size and weight of thestructure there is a greater energy absorption and cycle life.

The above description of the physical characteristics associated withthe thin-walled energy-absorbing elements of applicants invention hereinhas been presented to enable a more thorough understanding of theembodiments of applicants invention as hereinafter set forth.

For convenience, applicant prefers to define a thin-walledenergy-absorbing member as one in which the ratio of the wall thicknessto the outer diameter is one-tenth or less. Similarly, a thick-walledenergy-absorbing element is one in which the ratio of the wall thicknessto the outside diameter is greater than one-tenth.v However, as can beseen from FIG. 6, the physical characteristics are not sharply definedbut blend one into theother as the thickness of the wall with respect tothe outside diameter increases. Therefore, of course, in someapplications of applicants invention herein in utilizing the principlesas taught by applicant, it may be desirable to utilize two comparativelythick-walled elements nested one inside the other to providespecificenergy absorption characteristics for a given application.However, it will be appreciated that in the preferred embodiment ofapplicants invention, all of the energy-absorbing members are preferablythin-walled to provide the more linear strain distributions across thewall thickness.

. Referring now to FIG. 7, there isshown a perspective view of anenergy-absorbing arrangement generally designated 60 utilizing anenergy-absorbing element 62 according to the 1 principles of applicantsinvention herein. Asshown in FIG. 7,

the'energy-absorbing arrangement 60 comprises a first body member 64having a first bearing surface 66. There is also provided a second bodymember 68 having a second bearing surface 70 spaced a predetermineddistance fromthe first bearing surface 66 of the-first body member 64.As can be seen from FIG. 7, the first bearing surface 66 of the firstbody member 64, and the second bearingsurface 70 of the second bodymember .68, are substantially coextensive and overlap to define aparticular area therebetween. The second body member. 68 is adapted tomove relative to the first body member. 64 in the linear directionindicated by the arrow 72. That is, the second body member 68 is adaptedto move in both linear directions indicated by the arrow 72 under theinfluence of forces acting thereon.

The energy-absorbing element 62 is positioned between the first bodymember 64 and second body member 68 in an energy-absorbing cavity 65therebetween, and the energy-absorbing element 62 has an outerenergy-absorbing member 74 which, for example, may be similar to theouter energy-absorbing member 12 shown in FIGS. 1 and 2. Similarly, theenergy-absorbing element 62 also has a first inner energy-absorbingmember 76 positioned concentrically within the outer energy-absorbingmember 74 to have a common body member axis 78.

The outer energy-absorbing element 74 has an outer surface 80 that bearsagainst the first bearing surface 66 of the first body member 64 andsecond bearing surface 70 of the second body member 68, and theenergy-absorbing element 62 is adapted to roll between the first bearingsurface 66 and second bearing surface 70 for the condition of relativemotion of the second body member 68 in the directions indicated by thearrow 72.

As noted above, the outer energy-absorbing member 74 is similar to theouter energy-absorbing member 12 shown in FIGS. 1 and 2, and as such isa thin-walled cylindrical annular member having a first preselectedouter unstressed dimension to the outer surface 80 that is greater thanthe predetermined spacing between the first bearing surface 66 of thefirst body member 64 and second bearing surface 70 of the second bodymember 68. Therefore, the first body member 64 and second body member 68exert diametral compressive forces along a diameter of theenergy-absorbing element 62 in the direction indicated by the arrows 82.The diametral compressive forces, as illustrated by the arrows 82,subject the energy-absorbing element 62 to cyclic plastic deformationand, during the relative motion of the second body member 68 withrespect to the first body member 64 in the direction indicated by thearrow 72, the energy-absorbing element 62 undergoes rolling motiontherebetween and is therefore subjected to cyclic plastic deformation.

Since the unstressed diametral dimension to the outer surface 80 of theouter energy-absorbing member 74 is greater than the predeterminedspacing between the first bearing surface 66 of the first body member64, and second bearing surface 70 of the second body member 68 for theenergy-absorbing element 62 contained therebetween, the outerenergy-absorbing member 74 is diametrally dimensionally deformed to astressed condition by the forces indicated by the arrows 82 to a firstpreselected stressed outer diametral dimension that is less than thefirst preselected unstressed outer diametral dimension. Similarly, theouter energy-absorbing member 74 has an inner surface 84 that has afirst preselected unstressed diametral dimension that is greater thanthe inner-stressed dimension thereof when subjected to the diametralcompressive forces indicated by the arrows 82.

The inner energy-absorbing member 76 has an outer surface 86 that is insubstantially continuous contact with the inner surface 84 of the outerenergy-absrbing member 74 and, as noted above, may be similar to theinner energy-absorbing member 18 shown in FIGS. 1 and 2 and is,therefore, a thin-walled cylindrical annular duc,ile metalenergy-absorbing member that rolls with the outer energy-absorbingmember 74 about the common axis 78. The diametral compressive forces 82cause a diametral deformation of the inner energy-absorbing member 76.The inner energy-absorbing member 76 has a second preselected outerunstressed diametral dimension to the outer surface 86 thereof that issubstantially the same as the first preselected inner unstresseddiametral dimension to the inner surface 84 of the outerenergy-absorbing member 74. Similarly, the inner energy-absorbing member76 has a second preselected inner unstressed diametral dimension to theinner surface 88 thereof.

Under the influence of the diametral compressive forces 82, the outerenergy-absorbing member 74 diametrally deforms the innerenergy-absorbing element 76 to a second preselected outer stresseddiametral dimension to the outer surface 86 thereof that is less thanthe second preselected unstressed diametral dimension thereof, and asecond preselected inner stressed diametral dimension to the innersurface 88 thereof that is less than the second preselected unstressedinner diametral dimension.

Therefore, for the condition of the energy-absorbing element 62subjected to the diametrally compressive forces indicated by the arrows82 from the first body member 64 and second body member 68, during therelative motion of the second body member 68 with respect to the firstbody member 64 in the direction of the arrow 72, the energy-absorbingelement 62 and, therefore, the outer energy-absorbing member 74 andinner energy-absorbing member 76 roll about the preselected axis 78 inthe directions indicated by the arrow 90, and also, of course,translates in the directions indicated by the arrow 72 during therelative motion. Since both the outer energy-absorbing member 74 andinner energy-absorbing member 76 are deformed in the plastic deformationrange thereof, the rolling motion about the axis 78, as indicated by thearrow 90, produces cyclic plastic bending deformation for absorption ofthe energy associated with the relative movement of the second bodymember 68 with respect to the first body member 64.

A substantially incompressible, nondeformable, cylindrical member 92 maybe positioned interior the inner energy-absorbing member 76, and thecylindrical member 92 has a predetermined diametral dimension that isless than the unstressed inner diametral dimension of the innerenergy-absorbing member 76. The incompressible member 92 acts as a limitdevice for limiting the diametral deflection of the innerenergy-absorbing member 76, and, therefore, also the outerenergy-absorbing member 74. Applicant has found, as indicated in U.S.Pat. No. 3,435,919 that by limiting the amount of diametral deformation,the stress relieving plastic flow of the inner energy-absorbing member76 and outer energy-absorbing member 74 may be substantially eliminatedduring the times between utilization of the energy-absorbing device 60.It will be appreciated that similar incompressible nondeforrnablecylindrical members may be utilized in any of the embodiments ofapplicants invention described herein.

In the energy-absorbing element 10 shown in FIG. 1 and FIG. 3, and 62,shown in FIG. 7, there have been provided an outer energy-absorbingmember and an inner energy-absorbing member. Applicants invention hereinis not restricted to merely a nested arrangement of two energy-absorbingmembers but, it will be appreciated, that additional nestedenergyabsorbing members may be added as desired. FIG. 8 illustrates anenergy-absorbing element generally designated 100 comprised of an outerenergy-absorbing member 102 and a first inner energy absorbing member104. The outer energy-absorbing member 102 may be similar to the outerenergy-absorbing member 74, shown in FIG. 7, and the first innerenergy-absorbing member 104 may be similar to the inner energyabsorbingmember 76, shown in FIG. 7.

However, in the energy-absorbing element 100, there is also provided aplurality of secondary ductile metal, thin-walled, cylindrical annularenergy-absorbing members 106 and 108. Thus, in the embodiment ofapplicant's invention shown in FIG. 8, the energy-absorbing element 100has four thinwalled, ductile metal, cylindrical annular energy-absorbingmembers concentrically mounted together about a common body axis 110 insequential surface contact. That is, the outer surface of each of theinner energy-absorbing member 104 and plurality of secondaryenergy-absorbing members 106 and 108 are in substantially continuoussurface contact with the inner surface of the outer energy-absorbingmember 102, inner energy-absorbingmember 104 and secondaryenergyabsorbing members 106, respectively. The energy-absorbingarrangement 100 showing the four energy-absorbing members 102, 104, 106and 108 is not a limitation upon the number of similar energy-absorbingmembers that may be assemblied in a nested arrangement. It will beappreciated that greater than four may also be utilized for applicationsas may be desired.

The energy-absorbing element may be utilized in place of theenergy-absorbing element 62 shown in FIG. 7 and,

when subjected to diametral compressive forces as indicated in by thearrows 112, would be subjected to plastic deformation, and duringrelative movement 'of the body members applying the plastic deformationforces 112, would be subjected to cyclic plastic deformation to absorbthe energy associated with such relative movement.

In the embodiment of applicants energy-absorbing arrangements describedabove, it can be seen that the energy-absorbing elements are generallycylindrical and tubular. Applicants invention may also be utilized inother arrangements wherein the energy-absorbing elements are in the formof a toroid. FIGS. 9 and illustrate one such embodiment of applicantsinvention generally designated 120. As shown in FIGS. 9 and 10, theenergy-absorbing arrangement 120 is comprised of a first body member 122having a first bearing surface 124. The surface 124 comprises agenerally cylindrical surface. For convenience, it may be consideredthat the first body member 122 is fixed.

A second body member 126 having a bearing surface 128 which, in thisembodiment of applicant's invention is an outer peripheral surface ofthe generally cylindrical member 126. The second body member 126 isconcentrically mounted on axis 130 with the first body member 122. Thesecond body member 126 is adapted to move in linear directions asindicated by the arrow 132 with respect to the first body member 124,such movement being parallel to the common axis 130.

There is defined between the first bearing surface 124 and secondbearing surface 128 an annular energy-absorbing element receiving cavity134. A plurality of energy-absorbing elements 136 are positioned in theannular energy-absorbing element receiving cavity 134 and, as shown onFIG. 9, are arranged in three energy-absorbing element rows 136a, 136band 136c. In this embodiment of applicants invention, each of theenergy-absorbing rows is comprised of a plurality of theenergy-absorbing elements 136 which, as shown more clearly in FIG. 10,are a plurality of ring-type energy-absorbing elements according to theprinciples of applicants invention herein. That is, eachenergy-absorbing element 136 is comprised of an outer energy-absorbingelement 138 and an inner energy-absorbing element 140. The outerenergy-absorbing element 138 may be similar to the outerenergy-absorbing element 12 described above in connection with FIGS. 1and 2, and the inner energy-absorbing element 140 may be similar to theinner energy-absorbing element 18 described above in connection withFIGS. 1 and 2. However, in the arrangement shown in FIGS. 9 and 10, theaxial length of the energy-absorbing members 138 and 140 is equal to orless than the outer unstressed diametral dimension to the outer surface142 of the outer energy-absorbing member 138. Thus, within thedefinition above specified, the energy-absorbing elements 136 may beconsidered to be ring-type energy-absorbing elements. The innerenergy-absorbing member 140 is concentrically positioned within theouter energy-absorbing member in each of the energy-absorbing elements136 and is adapted to roll therewith about their common axis, and eachhas its outer surface in substantially continuous contact with the innersurface of the outer energy-absorbing member 138. The outerenergyabsorbing member 138 has an unstressed diametral dimension to theouter surface 142 thereof that is greater than the predetermined annularspacing indicated by the letter s in FIG. 9 between the first bearingsurface 124 on the first body member 122 and the second bearing s$rface128 on the second body member 126. Therefore, each of the outerenergy-absorbing members 138 and inner energy-absorbing members 140 ofeach of the energy-absorbing elements 136 are diametrally compressedalong a diameter thereof to be plastically deformed and, during therelative movement of the second body member 126 relative to the firstbody member 124 in the directions indicated by the arrow 132, each ofthe energy-absorbing elements 136 rolls about its common axis and,therefore, undergoes'cyclic plastic bending deformation for theabsorption of energy during such motion.

If desired, a substantially incompressible, nondeformable annularretainer member may be positioned within the inner energy-absorbingelement 140 to limit the amount of diametral deformation thereof andprevent plastic flow and creep in a manner similar to the member 92shown in FIG. 7.

Since each of the inner energy-absorbing elements 140 and outerenergy-absorbing elements 138 are thin-walled ringlike members, there isa comparatively large energy absorption per unit weight of energyabsorption element 136 due to the thinwalled stress-strain relationshipas described above in connection with FIG. 6. In modifications of thisembodiment, there may be provided a plurality of outer energy-absorbingmembers on each inner energy-absorbing member wherein the outerenergy-absorbing members have an axial length less than the axial lengthof the inner energy-absorbing member.

It will be appreciated that for linear stroke arrangements such as thatillustrated in FIGS. 9 and 10, or, as described below, for rotary strokeenergy-absorbing arrangements, applicants invention herein alsocomprises utilization of a plurality of inner energy-absorbingarrangements. FIG. 11 illustrates one such embodiment of applicant'sinvention generally designated 160. In the energy-absorbing arrangementwhich, generally, may be a linear stroke arrangement similar to theenergy-absorbing arrangement 120 shown in FIGS. 9 and 10, there isprovided a first body member 162 having a first bearing surface 164 thatmay be similar, respectively, to the first body member 122 and firstbearing surface 124 described above. Similarly, a second body member 166having a second bearing surface 168 is provided and may be similar tothe second body member 126 and second bearing surface 128 describedabove. There is provided an annular energy-absorbing element receivingcavity 172 between the first bearing surface 164 and second bearingsurface 168, and they are spaced apart a distance s. The second bodymember 166 is adapted to move linearly with respect to the first bodymember 162 in directions into and out of the plane of the paper.

A plurality of energy-absorbing elements 170 are contained in theannular space 172 between the first bearing surface 164 and secondbearing surface 168. Each of the energy-absorbing elements 170 iscomprised of an outer, thin-walled, cylindrical, ringlike, annular,ductile metal energy-absorbing member 174 which, in this embodiment ofapplicants invention, has an axial-length-to-outer-diameter-ratio lessthan one and, therefore, as described above, may be considered a ring174. The outer energy-absorbing member 174 has a first preselected outerunstressed diametral dimension to an outer surface 175 thereof that isgreater than the spacing s and, therefore, the outer energy-absorbingmember 174 is subjected to a diametrally compressive force between thefirst bearing surface 164 and the second bearing surface 168 that, forthe position shown in FIG. 11, deforms the outer energy-absorbing member174 in the plastic deformation range thereof.

The outer surface 175 of the outer energy-absorbing member 174 isadapted to roll on the first bearing surface 164 and second bearingsurface 168 during the above-described relative motion between the firstbody member 162 and second body member 166. A first innerenergy-absorbing member 176 is also a thin-walled, cylindrical, ringlikeannular ductile metal member and, as noted above, may be considered, inthis embodiment of applicants invention, a ring member. The first innerenergy-absorbing member 176 has a predetermined wall thickness and anaxial length coextensive with the axial length of the outerenergy-absorbing member 174. The inner energy-absorbing member 176 isconcentrically mounted about a common body axis 180 with the outerenergy-absorbing member 174 and has an outer surface in substantiallycontinuous contact with the inner surface of the outer energy-absorbingmember 174. Consequently, as described above, the inner energy-absorbingmember 176 is also diametrally compressed in the plastic deformationregion thereof by the diametral forces exerted on the outerenergyabsorbing member 174 from the first body member 162 and secondbody member 166. Therefore, during rolling of the energy-absorbingelement 170 about the common body axis 180. both the outerenergy-absorbing member 174 and inner energy-absorbing member 176undergo cyclic plastic bending deformation and thereby absorb energyduring the abovedescribed relative movement between the first bodymember 162 and second body member 166.

In the energy-absorbing arrangement 160 shown in FIG. 11, there are alsoprovided a plurality of secondary ductile metal, thin-walled,cylindrical ringlike, annular energy-absorbing members 182 and 184 thatare concentrically mounted together and in substantial sequentialsurface contact and mounted interior the inner energy-absorbing member176 for concentric mounting on the common body axis 180. Each of thesecondary energy-absorbing members 182 and 184 in each of theenergy-absorbing elements 170 have substantially coextensive axiallengths with the outer energy-absorbing member 174 and innerenergy-absorbing member 176. Each of the secondary energy-absorbingmembers 182 and 184 are diametrally compressed in the plasticdeformation region thereof and roll with the outer energy-absorbingmember 174 and the inner energy-absorbing member 176 about the commonbody axis 180, and in such rolling absorb energy by the cyclic plasticdeformation thereof.

A substantially incompressible, nondeformable, toroidal retainer member186 may be utilized, if desired, to limit the amount of diametraldeformation of the energy-absorbing element 170 in a manner similar tothe member 150 shown in FIG. and described above.

Applicant has found that in some applications of applicants inventionherein, such as the arrangement shown in FIG. 11, there may be atendency under some operational conditions for the innerenergy-absorbing member 176 and/or secondary energy-absorbing members182 and 184 to leave their coextensive axial positions with the outerenergy-absorbing element 174 and be dislodged therefrom. Accordingly,applicant prefers to utilize a restraining means to hold all of theenergyabsorbing members in the above-described axially aligned conditionto prevent axial migration. One arrangement for a restraining means isillustrated in FIG. 11 wherein the wall thicknesses of adjacentcorresponding energy-absorbing members of adjacent energy-absorbingelements are varied so that axial migration of any one energy-absorbingmember is substantially precluded. Thus, in the energy-absorbing element170a, the wall thickness of each of the energy-absorbing members 174,176, 182 and 184 may be different from the wall thickness of thecorresponding energy-absorbing members 174b, 176b, 182b and 184b in theenergy-absorbing element 170k. Thus, by staggering the wall thicknessesof the corresponding energy-absorbing members, axial translation of anyof the energy-absorbing members relative to the outer energy-absorbingmember is precluded.

The energy-absorbing element 170a, having similar energyabsorbingmembers to the energy-absorbing element 170a, may also be provided withenergy-absorbing members having the same wall thicknesses as theenergy-absorbing members 174, 176, 182 and 184 in energy-absorbingelement 170a. It will be appreciated that the angular divergence ofmembers 170a, 17012 and 170a has been exaggerated in FIG. 11 forillustrative purposes.

The use of multiple energy-absorbing elements is not confined to linearenergy-absorbing arrangements similar to those shown in FIGS. 9, 10 and11, wherein the action is akin to a piston in a cylinder. Rather,applicants invention herein may also be utilized in linearenergy-absorbing elements between two plates, as shown in FIG. 7,wherein a tubelike energy-absorbing element 162 was utilized. FIG. 12illustrates an embodiment of applicant's invention in which anenergy-absorbing arrangement, generally designated 190, is provided witha first body member 192 having a first bearing surface 194 and a secondbody member 196 having a second bearing surface 198. The first bodymember 192 and second body member 196 are, in this embodiment ofapplicant's invention, substantially coplanar, and the second bodymember 196 moves relative to the first body member 192 in directionsindicated by the arrow 200. The first body member 192 is spaced apreselected distance from the second body member 196 so that there is apredetermined spacing between the first bearing surface 194 and secondbearing surface 198, and a plurality of energy-absorbing elements 202are positioned in the space intermediate the first bearing surface 194and second bearing surface 198.

Each of the elements 202 may be similar to the energy-absorbing elements170, shown in FIG. 11, and may be comprised of an outer energy-absorbingmember 204, an inner energy-absorbing member 206 and a plurality ofsecondary energy-absorbing members 208 and 210. A rigid, nondeformable,cylindrical retainer member 212 may, if desired, be provided to limitthe diametral deformation of the energyabsorbing elements 202. Each ofthe energy-absorbing members 204, 206, 208 and 210 is concentricallymounted about a common body axis 214 and is adapted to roll on the firstbearing surface 194 and second bearing surface 198 during the relativemotion of the second body member 196, with respect to the first bodymember 192 in the direction indicated by the arrow 200. The outerenergy-absorbing member 204 has an unstressed diametral dimension thatis greater than the preselected spacing between the first bearingsurface 194 and second bearing surface 198 so that the outerenergy-absorbing member 204, inner energy-absorbing member 206 andplurality of secondary energy-absorbing members 208 and 210 arediametrally compressed in the plastic deformation region thereof by thefirst body member 192 and second body member 196 and, during theabove-described rolling action, undergo cyclic plastic deformationduring the relative movement of the second body member 196 with respectto the first body member 192. In order to prevent axial migration of anyof the energy-absorbing members 206, 208 or 210 with respect to theouter energy-absorbing member 204, applicant, in this embodiment ofapplicants invention, also prefers to utilize a retainer means. Asshown, there is provided a washerlike member 216 intermediate theenergy-absorbing element 202a and 202b. It will be appreciated thatsimilar washerlike members 216 may be positioned between other adjacentenergy-absorbing elements that are positioned within the space betweenthe first bearing surface 194 and second bearing surface 198.

In the embodiment of applicants invention as described above, applicanthas described the utilization of the improved energy-absorbing structurein linear motion energy-absorbing arrangements. It will be appreciated,of course, that applicant's invention is not limited to such linearenergy-absorbing arrangements but may equally well be utilized in rotaryenergy-absorbing arrangements. FIGS. 13 and 14 illustrate one embodimentof applicants invention, generally designated as 220, of such anenergy-absorbing arrangement in which there is provided a first bodymember 222 that is generally cylindrical and has an axis 224 and a firstbearing surface 226. Concentrically mounted about the axis 224 is thesecond body member 228 having a second bearing surface 230, and thesecond body member 228 is adapted to a move in a rotary direction asindicated by the arrow 232 about the common axis 224 with respect to thefirst body member 222. The first bearing surface 226 is spaced apreselected distance from the second bearing surface 230 and defines anannular energy-absorbing element receiving cavity 234 therebetween. Aplurality of energy-absorbing elements 236 are positioned in theenergy-absorbing element receiving cavity 234, and, in this embodimentof applicants invention, each of the energy-absorbing elements 236 hasan axis such as axis 238 that is parallel to the common axis 224. Whileany of the above-described types of energy-absorbing elements could beutilized as the energy-absorbing elements 236, in this embodiment ofapplicants invention, applicant shows an energy-absorbing element 236having a plurality of outer energy-absorbing members 240, eachcomprising a thin-walled, cylindrical, annular member having apreselected wall thickness and a first preselected axial length. In thisembodiment of applicants invention, each of the outer energy-absorbingelements 240 is similar and may, if desired, be a ring. It will beappreciated that applicant describes herein the details of theparticular energy-absorbing element 236a and that each of the otherenergy-absorbing elements 236 is similar thereto.

Each of the outer energy-absorbing members 240 has an outer surface thatis in rolling contact with the first bearing surface 226 and secondbearing surface 230. Further, each of the outer energy-absorbing members240 has a first preselected outer unstressed dimension to the outersurface thereof that is greater than the predetermined annular distancebetween the first bearing surface 226 and second bearing surface 228, sothat each of the outer energy-absorbing members 240 is diametrallydimensionally deformed in the plastic deformation range thereof to astressed condition by the first body member 222 and second body member228.

In each of the energy-absorbing elements 236, there is also provided aninner energy-absorbing member 242 that is concentrically mounted aboutthe common axis 238 thereof, and

I the inner energy-absorbing member 242 is a thin-walled,

cylindrical tubelike annular ductile metal member having a secondpreselected wall thickness and a second preselected axial length. Inthis embodiment of applicants invention, as shown on FIG. 13, the axiallength of the inner energy-absorbing member 242 is much greater than theaxial length of any of the outer energy-absorbing members 240. Thus, theentire inner surface of each of the outer energy-absorbing members 240is in substantial continuous contact with the outer surface of the innerenergy-absorbing member 242 and, therefore, in at least the coextensivesurface contact regions therebetween, the inner energy-absorbing member242 is diametrally compressed by the outer energy-absorbing member to astressed diametral dimension that is less than the unstressed diametraldimension and thereby is deformed in the plastic deformation regionthereof.

In order to prevent axial migration of any of the outer energy-absorbingmembers 240, it will be appreciated that retainer means may be utilized.As shown in FIGS. 13 and 14, applicant prefers to include cylindricalretainer members 244 in the first end 246 and in the second end 248 ofthe energy-absorbing arrangement 220, and retainers 244 may be a pressfit against the bearing surface 230. A plurality of tubelike retainermembers 250 may be positioned intermediate each of the adjacent outerenergy-absorbing members 240. The tubelike members 250 are not subjectedto a stressed loading and are not intended in this embodiment ofapplicant's invention to be an energy-absorbing member. The function ofthe tubelike members 250 is merely to retain the desired axial positionof each of the outer energy-absorbing members 240 on the innerenergy-absorbing member 242.

A rack member 252 engages the second body member 228 and rotates it inthe direction indicated by the arrow 232. During this rotationalmovement of the second body member 228 with respect to the first bodymember 222, each of the energyabsorbing elements 236 is rotated aboutits common axis 238 and rolls on the first bearing surface 226 andsecond bearing surface 230, and thus each of the outer energy-absorbingmembers 240 and inner energy-absorbing members 242 is subjected tocyclic plastic deformation during the rolling motion and absorbs energyassociated with the rotary relative motion of the second body member 228with respect to first body member 222. A reset arrangement, such asdescribed in US. Pat. No. 3,426,869 may be provided, if desired.

It will be appreciated that many variations in the combinations of axiallength and axial number of nested energy-absorbing members may beprovided as desired. For example, FIG. I illustrates an energy-absorbingelement 260 which could be utilized in the embodiment of applicant'sinvention shown in FIGS. 13 and 14 in place of the energy-absorbingelement 236. The energyabsorbing element 260 has a plurality of outerenergy-absorbing members 262 which may be similar to the outerenergy-absorbing members 240, and an inner energy-absorbing member 264which may be similar to the inner energy-absorbing member 242 shown inFIG. 13. However, in this embodiment of applicant's invention, there isalso provided a plurality of secondary energy-absorbing mem bers 266which are positioned interior the inner energy-absorbing member 264 insubstantially continuous surface contact therewith.

When the energy-absorbing element 260 is subjected to diametrallydirected compressive forces, each of the energyabsorbing members 262,264 and 266 is diametrally compressed in the plastic deformation regionthereof and is subjected to a rolling motion and undergoes cyclicplastic deformation for the absorption of energy. It can be seen thatthe axial length of the outer energy-absorbing member 262 is less thanthe axial length of the inner energy-absorbing member 264 and, further,that the axial length of the secondary energyabsorbing members 266 maybe the same as the axial length of the outer energy-absorbing members262, or, if desired, they could be different lengths.

It will be appreciated that the energy-absorbing members in anenergy-absorbing element for use in a rotary energy-absorbing structure,such as shown in FIGS. 13, 14 and 15, could all be of substantially thesame axial length. FIG. 16 illustrates such an energy-absorbing elementgenerally designated 270 in which there is provided an outerenergy-absorbing member 272, an inner energy-absorbing member 274 and asecondary energy-absorbing member 276, each of which may be thinwalled,cylindrical, tubelike, annular and energy-absorbing members insequential surface contact. A cylindrical rigid nondeformable retainermember 278 may, if desired, be provided in the energy-absorbing element270 to limit the diametral deformation of the energy-absorbing members272, 274 and 276. In this embodiment of applicants invention, each ofthe energy-absorbing members 272, 274 and 276 may be considered tubularrather than ringlike and, when subjected to diametrally compressiveforces, undergo a plastic deformation, and, when rotated about theircommon axis 280, undergo cyclic plastic deformation for the absorptionof ener- 8)- This concludes the description of applicants invention ofthe improved energy-absorbing arrangement. From the above, it can beseen that applicant has provided an improved energyabsorbing arrangementin which a much higher energy absorption per unit weight can be providedby the plurality of thinwalled energy-absorbing members than in anequivalent wall thickness single-walled element. As a result, there is amore linear strain distribution having a much lower slope on the rollingforce-diametral deformation curve. Therefore, the energy-absorbingarrangements may be fabricated with comparatively wide tolerances andare comparatively insensitive to tolerance variations. Further,utilization of a plurality of thin-walled energy-absorbing elementsprovides a much greater deflection for a given squeeze force and,therefore, much greater energy absorption for the same squeeze forceproviding the diametral compressive deformation thereof. Conversely, forthe same energy absorption capability, lower squeeze forces are requiredfor a plurality of nested thinwalled energy-absorbing structures thanfor a single thickwalled energy-absorbing structure.

It will be appreciated that, while applicant has described the outersurface of the inner energy-absorbing members as being in substantiallycontinuous surface contact with the inner surface of the outerenergy-absorbing member, the greater the deflection of theenergy-absorbing element and corresponding deformation into an ovalshape, the region of surface contact is concentrated along the minoraxis of such an oval shape and there may be little or no surface contactin regions along the major axis. Such a phenomena also may occur in thesecondary energy-absorbing elements. However, it is the regions in whichthere is surface contact that provides the transmission of the forcesfrom the outer to the inner and/or secondary energy-absorbing members.

What is claimed is:

1. ln an energy-absorbing arrangement of the type adapted to absorbenergy by cyclic plastic deformation, the improvement comprising, incombination:

a first body member having a first bearing surface;

diametral dimension to said inner surface less than said secondpreselected unstressed outer diametral dimension and second preselectedunstressed 'inner diametral dimension, respectively; and

a Second y member having a Second bearing Surface said at least oneouter energy-absorbing member and said at spaced a predetermineddistance from said first bearing least a first inner energy-absorbingmember. for the consurface on said first body member to define anenergy-abdition of said rolling motion thereof, is subjected to cyclicsorbing element receiving cavity thercbetween; plastic deformationduring said relative motion between at least a first portion of saidsecond bearing surface coexid fi b d member nd aid e o d body member intensive with a first portion of said first bearing surface to said firstpreselected direction. define an o rl p p r i n there-between, n said on2. The arrangement defined in claim 1, wherein said first body memberfor relative movement in a preselected energy-absorbing element furthercomprises: dir ti at to a first y member; a plurality of secondaryductile metal, thinwalled, cylindria first energy-absorbing elementcomprising: cal, tubelike, annular energy-absorbing members concenatleast one outer energy-absorbing member Positioned l5 trically mountedtogether and in sequential surface conintermediate said first bearingsurface of said first body tact; member and second bearing surface OfSCCOl'ld each of aid plurality of econdary energy absgrbing membodymember in sai overl p r f r r g motion bers having preselected wallthicknesses thereof and between said first body member and said secondbody preselected axial lengths; member for the condition of saidrelative movement of said plurality of secondary energy-absorbingmembers consaid Second body m mber with respect t aid firs centricallypositioned in said first inner energy-absorbing body member in id pr lir n, n s i at member for diametral plastic deformation for thecondileast one outer energy-absorbing member comprising: ti f id fi tinner energy-absorbing -mernber a thin-walled, cylindrical, tubelikeannular ductile metal diametrally deformed; =1

member having a first preselected wall thickness and a a first of aidplurality of secondary energy-absorbing memfi pres axial leng h; bershaving an outer surface portion thereof in contact an Outer Surface r lg engagement with Said first and with said inner surface of said firstinner energy-absorbing said second bearing surfaces of said first bodymember me b and Said Second y member r p ly; said plurality of secondaryenergy-absorbing members an inner Surface; rolling about the common axisfor the condition of said at a first preselected outer unstresseddiametral dimension h one outer energy-absorbing member d id fi t0 saidouter surface greater than said predetermined inner energy-absorbingmember rolling between said first. distance between said first bearingsurface and said b d member d id second body ber; d Second bearingSurface; said rolling motion of said plurality of secondary energy-abafirst preselected inner unstressed diametral dimension sorbing membersproviding cyclic plastic bending d f to said inner Surface; mation toeach of said plurality of secondary energy-ab- Said at least one outerenergy-absorbing member sorbing members for absorbing energy during saidrolling diametrally dimensionally deformed to a stressed conditi h fition by said first body member and said second body 3. The arrangementdefined in claim 1, wherein: member and having a first preselected outerstressed the ratio of said first preselected wall thickness of said atdiametral dimension less than said first preselected unleast one outerenergy-absorbing member to said unstressed outer diametral dimensionandafirst preselected stressed diametral outer dimension thereof is lessthan inner stressed dimension less than said first preselectedone-tenth; and inner stressed dimension less than said first preselectedthe ratio of said second preselected wall thickness of said innerunstressed dimension, and said at least one outer first innerenergy-absorbing member to said unstressed energy-absorbing memberhaving a first preselected stress outer diametral dimension thereof isless than one-tenth. and strain distribution therearound; 4. Thearrangement defined in claim 3, wherein: at least a first innerenergy-absorbing member concentrithe ratio of said first preselectedaxial length of said at least cally positioned within said at least oneouter energy-abone outer energy-absorbing member to said unstressedsorbing member for rolling motion about the common outer diametraldimension of said outer energy-absorbing axis with said at least oneouter energy-absorbing member is on the order of 1.0. member, and saidfirst inner energy-absorbing member 5. The arrangement defined in claim1, wherein said first comprising: axial length of said outerenergy-absorbing member is less a thin-walled, cylindrical, tubelike,annular, ductile metal than said second axial length of said first innerenergy-absorbmember having a second preselected wall thickness ingmember, and said first energy-absorbing element further and a secondpreselected axial length; comprising:

an outer surface in contact with said inner surface of said a pluralityof other outer energy-absorbing members, subat least one outerenergy-absorbing member; stantially identical to said at least one outerenergy-aban inner surface; sorbing member, and said plurality of otherouter energya second preselected outer unstressed diametraldimenabsorbing members concentrically mounted on said first sion to saidouter surface substantially the same assaid inner energy-absorbingmember in spaced apart relationfirst preselected inner unstresseddiametral dimension ship to each other and to said at least one outerenergyof said at least one outer energy-absorbing member; 5 absorbingmember; and

a second preselected inner unstressed diametral dimenmeans forrestraining said at least one outer energy-absorbsion to said innersurface; ing member and said other outer energy-absorbing memsaid atleast one outer energy-absorbing member bers in said preselected spacedarray.

diametrally deforming said first inner energy-absorbing 6. Thearrangement defined in claim 2 and further comprismember, for thecondition of said at least one outer enering:

gy-absorbing member diametrally deformed to said first a plurality ofother energy-absorbing elements, each of said preselected outer-stresseddiametral dimension and said plurality of other energy-absorbingelementscomprising:

first preselected inner-stressed diametral dimension to a a plurality ofother outer energy-absorbing members, an

second preselected outer-stressed diametral dimension to other innerenergy-absorbing member and a plurality of said outer surface and asecond preselected inner stressed other secondary absorbing membersconcentrically mounted substantially similarly to said concentricmounting of said at least one outer energy-absorbing member, said firstinner energy-absorbing member and said plurality of secondaryenergy-absorbing members, and in a preselected spaced array with eachother and with said first energy-absorbing element having said at leastone outer energy-absorbing member, said first inner energy-absorbingmember and said plurality of secondary energy-absorbing members.

7. The arrangement defined in claim 1 and further comprising:

ing member, and the ratio of said first preselected axial length of saidouter energy-absorbing member to said unstressed outer diametraldimension thereof is less than 1.0.

9. The arrangement defined in claim 1, wherein:

said first preselected axial length of said outer energy-absorbingmember is different from said second preselected axial length of saidfirst inner energy-absorbing member, and the ratio of said firstpreselected axial length of said outer energy-absorbing member to saidunstressed outer diametral dimension thereof is on the order of l .0.

10. The arrangement defined in claim 2, wherein:

said first preselected axial length of said at least one outerenergy-absorbing member, said second preselected axial length of saidfirst inner energy-absorbing member, and said preselected axial lengthsof said plurality of secondary energy-absorbing members aresubstantially identical, and the ratio of said first preselected axiallength of said at least one outer energy-absorbing member to said firstpreselected unstressed outer diametral dimension thereof is on the orderof l .0.

11. The arrangement defined in claim 2, wherein:

said first preselected axial length of said at least one outerenergy-absorbing member is different from said second preselected axiallength of said first inner energy-absorbing member, and said preselectedaxial lengths of each of said plurality of secondary energy-absorbingmembers is different from each of said first and said second preselectedaxial lengths, and the ratio of said first preselected axial length ofsaid at least one outer energyabsorbing member to said first preselectedunstressed outer diametral dimension thereof is on the order of 1.0.

12. The arrangement defined in claim 2, and further comprising:

a substantially incompressible nondeformable cylindrical memberpositioned within the smallest of said plurality of secondaryenergy-absorbing members and having a predetermined diametral dimensionthereof less than the unstressed inner diametral dimension of saidsmallest of said plurality of secondary energy-absorbing members forlimiting the diametral deformation of said outer energyabsorbing member,said first inner energy-absorbing member and said plurality of secondaryenergy-absorbing members to prevent stress relieving plastic flowthereof.

13. The arrangement defined in claim 2, wherein:

the ratio of said first preselected wall thickness of said at least oneouter energy-absorbing member to said first preselected unstressed outerdiametral dimension is less than 0.1;

the ratio of said second preselected wall thickness of said innerenergy-absorbing member to said second preselected unstressed outerdiametral dimension thereof is less than 0.1 and the ratio of wallthicknesses of each of said plurality of said secondary energy-absorbingmembers to the corresponding outer unstressed diametral dimensionsthereof are less than 0.1.

14. The arrangement defined in claim 6, wherein:

said wall thickness of each of said plurality of other outerenergy-absorbing members and said at least one outer energy-absorbingmember is different from the wall thickness of adjacent other outerenergy-absorbing members;

said wall thicknesses of said first inner energy-absorbing member andsaid plurality of other inner energy-absorbing members are differentfrom said wall thicknesses of adjacent other inner energy-absorbingmembers; and

said wall thickness of each of said plurality of secondaryenergy-absorbing members is different from said wall thickness ofcorresponding adjacent other secondary energy-absorbing members.

15. The arrangement defined in claim 6 and further comprising:

restraining means for restraining said plurality of other,

outer energy-absorbing members, other inner energy-absorbing members andplurality of other secondary inner energy-absorbing members; and

said at least one outer energy-absorbing member, said first innerenergy-absorbing member and said plurality of secondary innerenergy-absorbing members in said concentric mounting and saidpreselected spaced array.

16. The arrangement defined in claim 15, wherein:

said restraining means comprises a plurality of disc means mountedintermediate each of said energy-absorbing elements, and each of saidplurality of disc means having an outer dimension less than said firstpreselected stressed outer dimension of said outer energy-absorbingmember.

17. The arrangement defined in claim 1, wherein:

said preselected direction of movement of said second body member withrespect to said first body member is linear.

18. The arrangement defined in claim 1, wherein:

said preselected direction of movement of said second body member withrespect to said first body member is rotary.v

19. The arrangement defined in claim 17, wherein:

said first body member comprises first flat platelike member and saidfirst bearing surface is planar; and

said second body member comprises a second flat platelike member andsaid second bearing surface is planar.

20. The arrangement defined in claim 17, wherein:

said first body member comprises a tubular member having an outersurface and an inner surface, and said first bearing surface comprisessaid inner surface thereof;

said second body member comprises a cylindrical member having an outerperipheral surface, and said second bearing surface comprises said outerperipheral surface thereof;

said energy-absorbing element cavity comprises an annular cavity betweensaid outer peripheral surface of said second body member and said innersurface of said first body member;

said first body member is concentrically mounted on said second bodymember and said first body member and said second body member having acommon body member axis; and.

said preselected direction is parallel to said common body axis.

21. The arrangement defined in claim 5 and further comprising:

aplurality of other energy-absorbing elements, each comprising: an otherinner energy-absorbing member similar to said first innerenergy-absorbing member mounted in a spaced array with each other andwith said first energyabsorbing element in said energy-absorbing elementreceiving cavity; plurality of other outer energy-absorbing members,each of said other outer energy-absorbing members similar to said atleast one outer energy-absorbing member, and mounted on each of saidplurality of other inner energy-absorbing members in said preselectedspaced array; and means for restricting each of said other outerenergy-absorbing members on each of said plurality of other innerenergy-absorbing members in said preselected spaced array. 22. Thearrangement defined in claim 21, wherein: said first body membercomprises a tubular member having an outer surface and an inner surface,and said first bearing surface comprises said inner surface thereof;said second body member comprises a cylindrical body member having anouter peripheral surface and said second bearing surface comprises saidouter peripheral surface thereof;

said energy-absorbing element cavity comprises an annular cavityintermediate said outer peripheral surface of said second body memberand said inner surface of said first body member;

said first body member is concentrically mounted on said second bodymember and said first body member and said second body member having acommon body member axis; and

said preselected direction is linear and parallel to said common bodyaxis.

23. The arrangement defined in claim 20, wherein:

said preselected direction of movement of said second body member withrespect to said first body member is rotary.

1. In an energy-absorbing arrangement of the type adapted to absorb energy by cyclic plastic deformation, the improvement comprising, in combination: a first body member having a first bearing surface; a second body member having a second bearing surface spaced a predetermined distance from said first bearing surface on said first body member to define an energy-absorbing element receiving cavity therebetween; at least a first portion of said second bearing surface coextensive with a first portion of said first bearing surface to define an overlap portion therebetween, and said second body member for relative movement in a preselected direction relative to said first body member; a first energy-absorbing element comprising: at least one outer energy-absorbing member positioned intermediate said first bearing surface of said first body member and said second bearing surface of said second body member in said overlap area for rolling motion between said first body member and said second body member for the condition of said relative movement of said second body member with respect to said first body member in said preselected direction, and said at least one outer energy-absorbing member comprising: a thin-walled, cylindrical, tubelike annular ductile metal member having a first preselected wall thickness and a first preselected axial length; an outer surface for rolling engagement with said first and said second bearing surfaces of said first body member and said second body member respectively; an inner surface; a first preselected outer unstressed diametral dimension to said outer surface greater than said predetermined distance between said first bearing surface and said second bearing surface; a first preselected inner unstressed diametral dimension to said inner surface; said at least one outer energy-absorbing member diametrally dimensionally deformed to a stressed condition by said first body member and said second body member and having a first preselected outer stressed diametral dimension less than said first preselected unstressed outer diametral dimension and a first preselected inner stressed dimension less than said first preselected inner stressed dimension less than said first preselected inner unstressed dimension, and said at least one outer energy-absorbing member having a first preselected stress and strain distribution therearound; at least a first inner energy-absorbing member concentrically positioned within said at least one outer energy-absorbing member for rolling motion about the common axis with said at least one outer energy-absorbing member, and said first inner energy-absorbing member comprising: a thin-walled, cylindrical, tubelike, annular, ductile metal member having a second preselected wall thickness and a second preselected axial length; an outer surface in contact with said inner surface of said at least one outer energy-absorbing member; an inner surface; a second preselected outer unstressed diametral dimension to said outer surface substantially the same as said first preselected inner unstressed diametral dimension of said at least one outer energy-absorbing member; a second preselected inner unstressed diametral dimension to said inner surface; said at least one outer energy-absorbing member diametrally deforming said first inner energy-absorbing membEr, for the condition of said at least one outer energy-absorbing member diametrally deformed to said first preselected outer-stressed diametral dimension and said first preselected inner-stressed diametral dimension to a second preselected outer-stressed diametral dimension to said outer surface and a second preselected inner stressed diametral dimension to said inner surface less than said second preselected unstressed outer diametral dimension and second preselected unstressed inner diametral dimension, respectively; and said at least one outer energy-absorbing member and said at least a first inner energy-absorbing member, for the condition of said rolling motion thereof, is subjected to cyclic plastic deformation during said relative motion between said first body member and said second body member in said first preselected direction.
 2. The arrangement defined in claim 1, wherein said first energy-absorbing element further comprises: a plurality of secondary ductile metal, thin-walled, cylindrical, tubelike, annular energy-absorbing members concentrically mounted together and in sequential surface contact; each of said plurality of secondary energy-absorbing members having preselected wall thicknesses thereof and preselected axial lengths; said plurality of secondary energy-absorbing members concentrically positioned in said first inner energy-absorbing member for diametral plastic deformation for the condition of said first inner energy-absorbing member diametrally deformed; a first of said plurality of secondary energy-absorbing members having an outer surface portion thereof in contact with said inner surface of said first inner energy-absorbing member; said plurality of secondary energy-absorbing members rolling about the common axis for the condition of said at least one outer energy-absorbing member and said first inner energy-absorbing member rolling between said first body member and said second body member; and said rolling motion of said plurality of secondary energy-absorbing members providing cyclic plastic bending deformation to each of said plurality of secondary energy-absorbing members for absorbing energy during said rolling motion thereof.
 3. The arrangement defined in claim 1, wherein: the ratio of said first preselected wall thickness of said at least one outer energy-absorbing member to said unstressed diametral outer dimension thereof is less than one-tenth; and the ratio of said second preselected wall thickness of said first inner energy-absorbing member to said unstressed outer diametral dimension thereof is less than one-tenth.
 4. The arrangement defined in claim 3, wherein: the ratio of said first preselected axial length of said at least one outer energy-absorbing member to said unstressed outer diametral dimension of said outer energy-absorbing member is on the order of 1.0.
 5. The arrangement defined in claim 1, wherein said first axial length of said outer energy-absorbing member is less than said second axial length of said first inner energy-absorbing member, and said first energy-absorbing element further comprising: a plurality of other outer energy-absorbing members, substantially identical to said at least one outer energy-absorbing member, and said plurality of other outer energy-absorbing members concentrically mounted on said first inner energy-absorbing member in spaced apart relationship to each other and to said at least one outer energy-absorbing member; and means for restraining said at least one outer energy-absorbing member and said other outer energy-absorbing members in said preselected spaced array.
 6. The arrangement defined in claim 2 and further comprising: a plurality of other energy-absorbing elements, each of said plurality of other energy-absorbing elements comprising: a plurality of other outer energy-absorbing members, an other inner energy-absorbing member and a plurality of other secondary absorbing members concentrically Mounted substantially similarly to said concentric mounting of said at least one outer energy-absorbing member, said first inner energy-absorbing member and said plurality of secondary energy-absorbing members, and in a preselected spaced array with each other and with said first energy-absorbing element having said at least one outer energy-absorbing member, said first inner energy-absorbing member and said plurality of secondary energy-absorbing members.
 7. The arrangement defined in claim 1 and further comprising: a substantially incompressible, nondeformable cylindrical member positioned within said first inner energy-absorbing member and having a predetermined diametral dimension less than said unstressed inner diametral dimension of said inner energy-absorbing member for limiting the diametral deformation of said at least one outer energy-absorbing member and said first inner energy-absorbing member to prevent stress relieving plastic flow thereof.
 8. The arrangement defined in claim 1, wherein: said first preselected axial length of said outer energy-absorbing member is substantially identical to said second preselected axial length of said first inner energy-absorbing member, and the ratio of said first preselected axial length of said outer energy-absorbing member to said unstressed outer diametral dimension thereof is less than 1.0.
 9. The arrangement defined in claim 1, wherein: said first preselected axial length of said outer energy-absorbing member is different from said second preselected axial length of said first inner energy-absorbing member, and the ratio of said first preselected axial length of said outer energy-absorbing member to said unstressed outer diametral dimension thereof is on the order of 1.0.
 10. The arrangement defined in claim 2, wherein: said first preselected axial length of said at least one outer energy-absorbing member, said second preselected axial length of said first inner energy-absorbing member, and said preselected axial lengths of said plurality of secondary energy-absorbing members are substantially identical, and the ratio of said first preselected axial length of said at least one outer energy-absorbing member to said first preselected unstressed outer diametral dimension thereof is on the order of 1.0.
 11. The arrangement defined in claim 2, wherein: said first preselected axial length of said at least one outer energy-absorbing member is different from said second preselected axial length of said first inner energy-absorbing member, and said preselected axial lengths of each of said plurality of secondary energy-absorbing members is different from each of said first and said second preselected axial lengths, and the ratio of said first preselected axial length of said at least one outer energy-absorbing member to said first preselected unstressed outer diametral dimension thereof is on the order of 1.0.
 12. The arrangement defined in claim 2, and further comprising: a substantially incompressible nondeformable cylindrical member positioned within the smallest of said plurality of secondary energy-absorbing members and having a predetermined diametral dimension thereof less than the unstressed inner diametral dimension of said smallest of said plurality of secondary energy-absorbing members for limiting the diametral deformation of said outer energy-absorbing member, said first inner energy-absorbing member and said plurality of secondary energy-absorbing members to prevent stress relieving plastic flow thereof.
 13. The arrangement defined in claim 2, wherein: the ratio of said first preselected wall thickness of said at least one outer energy-absorbing member to said first preselected unstressed outer diametral dimension is less than 0.1; the ratio of said second preselected wall thickness of said inner energy-absorbing member to said second preselected unstressed outer diametral dimension thereof is less than 0.1; and the ratio of wall tHicknesses of each of said plurality of said secondary energy-absorbing members to the corresponding outer unstressed diametral dimensions thereof are less than 0.1.
 14. The arrangement defined in claim 6, wherein: said wall thickness of each of said plurality of other outer energy-absorbing members and said at least one outer energy-absorbing member is different from the wall thickness of adjacent other outer energy-absorbing members; said wall thicknesses of said first inner energy-absorbing member and said plurality of other inner energy-absorbing members are different from said wall thicknesses of adjacent other inner energy-absorbing members; and said wall thickness of each of said plurality of secondary energy-absorbing members is different from said wall thickness of corresponding adjacent other secondary energy-absorbing members.
 15. The arrangement defined in claim 6 and further comprising: restraining means for restraining said plurality of other, outer energy-absorbing members, other inner energy-absorbing members and plurality of other secondary inner energy-absorbing members; and said at least one outer energy-absorbing member, said first inner energy-absorbing member and said plurality of secondary inner energy-absorbing members in said concentric mounting and said preselected spaced array.
 16. The arrangement defined in claim 15, wherein: said restraining means comprises a plurality of disc means mounted intermediate each of said energy-absorbing elements, and each of said plurality of disc means having an outer dimension less than said first preselected stressed outer dimension of said outer energy-absorbing member.
 17. The arrangement defined in claim 1, wherein: said preselected direction of movement of said second body member with respect to said first body member is linear.
 18. The arrangement defined in claim 1, wherein: said preselected direction of movement of said second body member with respect to said first body member is rotary.
 19. The arrangement defined in claim 17, wherein: said first body member comprises first flat platelike member and said first bearing surface is planar; and said second body member comprises a second flat platelike member and said second bearing surface is planar.
 20. The arrangement defined in claim 17, wherein: said first body member comprises a tubular member having an outer surface and an inner surface, and said first bearing surface comprises said inner surface thereof; said second body member comprises a cylindrical member having an outer peripheral surface, and said second bearing surface comprises said outer peripheral surface thereof; said energy-absorbing element cavity comprises an annular cavity between said outer peripheral surface of said second body member and said inner surface of said first body member; said first body member is concentrically mounted on said second body member and said first body member and said second body member having a common body member axis; and said preselected direction is parallel to said common body axis.
 21. The arrangement defined in claim 5 and further comprising: a plurality of other energy-absorbing elements, each comprising: an other inner energy-absorbing member similar to said first inner energy-absorbing member mounted in a spaced array with each other and with said first energy-absorbing element in said energy-absorbing element receiving cavity; a plurality of other outer energy-absorbing members, each of said other outer energy-absorbing members similar to said at least one outer energy-absorbing member, and mounted on each of said plurality of other inner energy-absorbing members in said preselected spaced array; and means for restricting each of said other outer energy-absorbing members on each of said plurality of other inner energy-absorbing members in said preselected spaced array.
 22. The arrangement defined in claim 21, wherein: said First body member comprises a tubular member having an outer surface and an inner surface, and said first bearing surface comprises said inner surface thereof; said second body member comprises a cylindrical body member having an outer peripheral surface and said second bearing surface comprises said outer peripheral surface thereof; said energy-absorbing element cavity comprises an annular cavity intermediate said outer peripheral surface of said second body member and said inner surface of said first body member; said first body member is concentrically mounted on said second body member and said first body member and said second body member having a common body member axis; and said preselected direction is linear and parallel to said common body axis.
 23. The arrangement defined in claim 20, wherein: said preselected direction of movement of said second body member with respect to said first body member is rotary. 